1. Field of the Invention
The present invention relates to an apparatus for manufacturing semiconductor devices. More particularly, the present invention relates to an ion implanting apparatus for manufacturing semiconductor devices.
2. Description of the Related Art
In a typical ion implanting process, P-type impurities such as boron (B), aluminum (Al) and indium (In), and N-type impurities such as antimony (Sb), phosphorus (P) and arsenic (As), are used to form a plasma ion beam. A semiconductor wafer is irradiated with the ion beam so that the impurities are implanted into crystalline structures of the wafer to produce desired levels of conductivity and resistivity in the implanted areas. The ion implanting process has widely been used in the manufacturing of semiconductor devices because it allows the concentration of the implanted impurities and hence, the levels of conductivity and resistivity, to be readily controlled.
The ion implanting apparatus generally includes an ionization unit, an analyzer unit, an acceleration unit, a focusing unit, a scanning unit, an implanting chamber, and a vacuum chamber.
However, processing defects may be caused by even fine particles in the ion implantation process. Accordingly, a very significant aspect of the process entails maintaining a high vacuum state within the wafer processing chamber. To this end, a vacuum gauge is used to measure the vacuum levels in the ionization unit, the analyzer unit, and the wafer processing chamber during the ion implanting process. An ionization vacuum gauge is mainly used as such a vacuum gauge. The ionization vacuum gauge measures the flow of positive ions ionized by electron collision (i.e., the gauge measures current). Ionization vacuum gauges may be classified as hot cathode ion gauges (HCIG) and cold cathode ion gauges (CCIG).
The analyzer unit analyzes positive ions having only a certain atomic weight by employing the operating principle of a mass spectrometer. The analyzer unit has a magnet to establish a magnetic field in proportion to the magnitude of current applied to the analyzer unit. The magnitude of the current is varied based on the type of ion. For example, in the case of boron (B) having an atom weight of xe2x80x9c11xe2x80x9d, current of 28-29A is supplied. In the case of phosphorus (P) having an atomic weight of xe2x80x9c31xe2x80x9d, current of 121-122A is supplied. Accordingly, when the ion to be analyzed is arsenic (As) having an atomic weight of xe2x80x9c75xe2x80x9d, a magnetic field of a very large magnitude is provided.
The magnetic field established by the magnet of the mass analyzer has an influence on the magnetic field in the cold cathode ion gauge for measuring the vacuum level inside the analyzer unit. If the magnetic field lines are in opposite directions, the cold cathode ion gauge is too unstable to be read correctly. If the magnetic field lines are in the same direction, the value read by the cold cathode ion gauge fluctuates so widely that the measured vacuum level is utterly unreliable. Furthermore, the superimposed magnetic fields cause the positive ions to deposit rapidly on the negative electrode of the cold cathode ion gauge, thereby reducing the lifespan of the cold cathode ion gauge.
An object of the present invention is to provide an ion implanting apparatus and in particular, a vacuum gauge for use therein, that is free of the problems and drawbacks of the prior art.
More specifically, one object of the present invention is to provide an ion implanting apparatus in which the vacuum level inside an analyzer unit may be measured without being influenced by a magnetic field generated by a magnet of the analyzer unit.
Another object of the present invention is to provide an ion implanting apparatus in which a large magnetic field may be established in a cold cathode ion gauge and yet the ions are not deposited rapidly onto an electrode of the cold cathode ion gauge, whereby the cold cathode ion gauge retains a long the lifespan.
To achieve these objects, the present invention provides the combination of a vacuum gauge for use in measuring the level of a vacuum within analyzer unit of an ion implanting apparatus, and a magnetic field shield for the vacuum gauge.
According to one aspect of the present invention, an ion implanting apparatus includes an ionization unit operative to produce an ion beam, an analyzer unit connected to said ionization unit downstream thereof in the apparatus and operative to analyze ions of the beam that are to be implanted into the substrate, a vacuum unit connected to the analyzing unit so as to create a vacuum within the analyzing unit, an implanting chamber connected to the analyzer unit downstream thereof in the apparatus, and the aforementioned vacuum gauge and shield for shielding the vacuum gauge from an external magnetic field such as that generated by a magnet of the analyzer unit.
The magnetic field shield has a plurality of shielding plates encircling the vacuum gauge, and dielectric material interposed between the shielding plates. Preferably, the shield is a cylindrical member. Also, the shield preferably has three concentric shielding plates.